Improve scope handling in finder class

ee/app/finders/security/vulnerability_findings_finder.rb

@@ -64,12 +64,15 @@ module Security
     end
 
     def init_collection(scope)
-      if scope == :all
+      case scope
+      when :all
         vulnerable.all_vulnerabilities
-      elsif scope == :with_sha
+      when :with_sha
         vulnerable.latest_vulnerabilities_with_sha
-      else
+      when :latest
         vulnerable.latest_vulnerabilities
+      else
+        raise ArgumentError, "invalid value for 'scope': #{scope}"
       end
     end
   end

ee/spec/finders/security/vulnerability_findings_finder_spec.rb

@@ -130,5 +130,31 @@ describe Security::VulnerabilityFindingsFinder do
         end
       end
     end
+
+    describe 'scope specifiers' do
+      using RSpec::Parameterized::TableSyntax
+
+      where(:scope) do
+        [
+          [:all],
+          [:with_sha],
+          [:latest]
+        ]
+      end
+
+      with_them do
+        it 'accepts the scope specifier as valid' do
+          expect { described_class.new(group).execute(scope) }.not_to raise_error
+        end
+      end
+
+      context 'with an invalid scope specifier' do
+        it 'raises error' do
+          expect { described_class.new(group).execute(:invalid) }.to(
+            raise_error(ArgumentError, "invalid value for 'scope': invalid")
+          )
+        end
+      end
+    end
   end
 end